Question

How many prepositional phrase are in the above sentence the old combine on the farm had not been operating in almost a decade but after a few hours of work it was operating flawlessly in the field

Answer 1

The old combine on the farm had not been operating in almost a decade, but after a few hours of work, it was operating flawlessly in the field.

on the farm -- prep phrase (adjective)
in almost a decade -- prep phrase (adverb)
after a few hours of work -- prep phrase (adverb)
in the field -- prep phrase (adverb)

So there are 4 prepositional phrases in this sentence.